1. Field of the Invention
The present invention relates to a hierarchical storage management system, device and program for carrying out inter-tier file migration that conforms to the way files are used.
2. Description of the Related Art
Hierarchical storage management (HSM) technology configures a plurality of file systems that is in storage systems with different functions and performance as a single file system, and migrates files between the file systems in accordance with the way the files are utilized.
Arranging a file that is accessed with high frequency in an upper Tier (a file system featuring high performance and bit costs) and arranging a file that is accessed with low frequency in a lower Tier (a file system featuring low performance and bit costs) reduces costs without lowering the performance of the system as a whole.
A patent document (2004/0193760 A1) discloses technology for exercising control so as to store file data in any of a plurality of storage areas in accordance with the file characteristics.
A patent document (JP-A-2001-101039) discloses technology for executing an inter-tier file migration from the upper Tier to the lower Tier when a file, which satisfies a certain set condition, i.e. a last file access time, a last file update time or a file size, is retrieved as a migration file, and this migration file satisfies a condition in which a remaining capacity has been set. In addition, the patent document (JP-A-2001-101039) also discloses technology by which a user application expressly specifies an inter-tier file migration by changing a file attribute, and the migration is executed at the time of the attribute change.
In the prior art, the problem is that an unnecessary file migration is carried out from the lower Tier to the upper Tier, delaying file access and straining the capacity of the upper Tier.
In a conventional HSM system, in a case where a lower-tier file is accessed even one time, this file is migrated to the upper Tier. In a conventional system, an unnecessary file migration to Tier 1 puts a strain on the capacity of Tier 1, and generates an I/O in line therewith. An unnecessary file migration is the migration of a low access frequency file, such as a file that a client opened by mistake, or a file that was opened during a file search.
With regard to this, the patent document (2004/0193760 A1) discloses a technology for carrying out an inter-tier file migration in accordance with the life cycle of the file. A file access count and other such statistical access information is held, but there is no disclosure as to a technology for utilizing the statistical access information in an inter-tier file migration.
Another problem with the prior art is that a file that is not meant to be migrated gets migrated.
In a case where the clipping of all migration candidate files is carried out based on a set condition, files, which were not supposed to be migrated, are migrated. These include files that are not desirable to migrate to the lower Tier, such as, for example, an important file, or a file for which a short response time is required, and files that are not desirable to migrate to the upper Tier, such as, for example, a large size file.
The patent document JP-A-2001-101039 discloses technology by which a user application expressly specifies an inter-tier file migration by changing a file attribute, and the migration is executed when the attribute changes. However, the problem is that in a case where the user application frequently issues migration instructions, inter-tier file migrations are carried out frequently and access performance declines. Another problem is that in a case where the user application does not issue a migration instruction very often, an inter-tier file migration is not carried out until the remaining capacity of the Tier drops to the set value, resulting in frequently accessed files not being migrated to the upper Tier and infrequently accessed files remaining in the upper Tier.